Method of laterally inserting an artificial vertebral disk replacement implant with curved spacer

ABSTRACT

In various embodiment of the invention an implant can be placed between two adjacent vertebral bodies using a lateral insertion method. The implant is characterized as having a first end plate and a second end plate which a crossbar spacer there between. The crossbar spacer preferably fits within a channel on the inner surfaces of the first end plate and the second end plate, where the spacer allows the first end plate to pivot, twist and/or rotate relative to the second end plate. The first end plate and the second end plate include a keel extending therefrom, where the keel traverses longitudinally between a first lateral side and a second opposed lateral side and is substantially perpendicular to the sagittal plane of the patient&#39;s spine.

CLAIM OF PRIORITY

This application claims priority to U.S. Provisional Patent Application No. 60/524,350, filed Nov. 21, 2003, entitled “ARTIFICIAL VERTEBRAL DISK REPLACEMENT IMPLANT WITH A SPACER AND LATERAL IMPLANT METHOD,” which is incorporated herein by reference.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to U.S. Provisional Application No. 60/422,039, filed Oct. 29, 2002, entitled “ARTIFICIAL VERTEBRAL DISK REPLACEMENT IMPLANT WITH TRANSLATING PIVOT POINT AND METHOD,” U.S. patent application Ser. No. 10/684,669, filed Oct. 14, 2003, entitled “ARTIFICIAL VERTEBRAL DISK REPLACEMENT IMPLANT WITH TRANSLATING PIVOT POINT AND METHOD,” U.S. Provisional Application No. 60/422,011, filed Oct. 29, 2002, entitled “TOOLS FOR IMPLANTING AN ARTIFICIAL VERTEBRAL DISK AND METHOD,” U.S. patent application Ser. No. 10/685,134, filed Oct. 14, 2003, entitled “TOOLS FOR IMPLANTING AN ARTIFICIAL VERTEBRAL DISK AND METHOD,” U.S. Provisional Application No. 60/422,022, filed Oct. 29, 2002, entitled “ARTIFICIAL VERTEBRAL DISK REPLACEMENT IMPLANT WITH A SPACER AND METHOD,” U.S. patent application Ser. No. 10/685,011, filed Oct. 14, 2003, entitled “ARTIFICIAL VERTEBRAL DISK REPLACEMENT IMPLANT WITH SPACER AND METHOD,” and U.S. Provisional Application No. 60/517,973, filed Nov. 6, 2003, entitled “ARTIFICIAL VERTEBRAL DISK REPLACEMENT IMPLANT WITH CROSSBAR SPACER AND LATERAL IMPLANT METHOD,” U.S. patent application Ser. No. 10/981,963, filed Nov. 5, 2005, entitled “LATERALLY INSERTABLE ARTIFICIAL VERTEBRAL DISK REPLACEMENT IMPLANT WITH TRANSLATING PIVOT POINT,” U.S. patent application Ser. No. 10/981,807, filed Nov. 5, 2005, entitled “METHOD OF LATERALLY INSERTING AN ARTIFICIAL VERTEBRAL DISK REPLACEMENT IMPLANT WITH TRANSLATING PIVOT POINT,” U.S. patent application Ser. No. 10/982,638, filed Nov. 5, 2005, entitled “LATERALLY INSERTABLE ARTIFICIAL VERTEBRAL DISK REPLACEMENT IMPLANT WITH A CROSSBAR SPACER,” U.S. patent application Ser. No. 10/981,952, filed Nov. 5, 2005, entitled “METHOD OF LATERALLY INSERTING ARTIFICIAL VERTEBRAL DISK REPLACEMENT IMPLANT WITH A CROSSBAR SPACER,” U.S. patent application Ser. No. 10/981,923, filed Nov. 5, 2005, entitled “LATERALLY INSERTABLE ARTIFICIAL VERTEBRAL DISK REPLACEMENT IMPLANT WITH A SPACER,” all of which are incorporated herein by reference.

FIELD OF ART

This field of art of this disclosure is directed to an artificial vertebral disk replacement and method.

BACKGROUND

The spinal column is a biomechanical structure composed primarily of ligaments, muscles, vertebrae and intervertebral disks. The biomechanical functions of the spine include: (1) support of the body, which involves the transfer of the weight and the bending movements of the head, trunk and arms to the pelvis and legs, (2) complex physiological motion between these parts, and (3) protection of the spinal cord and nerve roots.

As the present society ages, it is anticipated that there will be an increase in adverse spinal conditions which are characteristic of aging. For example, with aging comes an increase in spinal stenosis (including, but not limited to, central canal and lateral stenosis), and facet joint degeneration. Spinal stenosis typically results from the thickening of the bones that make up the spinal column and is characterized by a reduction in the available space for the passage of blood vessels and nerves. Facet joint degeneration results from the constant load borne by the facet joints, and the eventual wear that results. Pain associated with both conditions can be relieved by medication and/or surgery.

In addition, to spinal stenosis, and facet joint degeneration, the incidence of damage to the intervertebral disks is also common. The primary purpose of the intervertebral disk is to act as a shock absorber. The disk is constructed of an inner gel-like structure, the nucleus pulposus (the nucleus), and an outer rigid structure comprised of collagen fibers, the annulus fibrosus (the annulus). At birth, the disk is 80% water, and then gradually diminishes with time, becoming stiff. With age, disks may degenerate, and bulge, thin, herniate, or ossify. Additionally, damage to disks may occur as a result disease, trauma or injury to the spine.

The damage to disks may call for a range of restorative procedures. If the damage is not extensive, repair may be indicated, while extensive damage may indicate full replacement. Regarding the evolution of restoration of damage to intervertebral disks, rigid fixation procedures resulting in fusion are still the most commonly performed surgical intervention. However, trends suggest a move away from such procedures. Currently, areas evolving to address the shortcomings of fusion for remediation of disk damage include technologies and procedures that preserve or repair the annulus, that replace or repair the nucleus, and that advance implants for total disk replacement. The trend away from fusion is driven both by issues concerning the quality of life for those suffering from damaged intervertebral disks, as well as responsible health care management. These issues drive the desire for procedures that are minimally invasive, can be tolerated by patients of all ages, especially seniors, and can be performed preferably on an out patient basis.

Most recently, there has been an increased interest in total disk replacement technology. A number of artificial disks are beginning to appear in the medical device marketplace. These artificial disks vary greatly in shape, design and functionality. With these devices go tools and methods for insertion between vertebrae thereof. Though currently the most common method of insertion of disk replacement implants is the anterior approach, other surgical procedures, such as the lateral approach, are evolving.

Accordingly, there is a need in the art for innovation in technologies and methods that advance the art in the area of minimally invasive intervertebral disk replacement. This not only enhances the quality of life for those suffering from the condition, but is responsive to the current needs of health care management.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a side perspective view of an embodiment of the assembled implant 100. FIG. 1B is an alternative side perspective view of an embodiment of the assembled implant 100.

FIG. 2A and FIG. 2B show perspective views of the first and second inner surfaces of the first end plate and the second end plate of an embodiment of implant 100. FIG. 2C through FIG. 2F show cross-sectional views of the first end plate and the second end plate of an embodiment of implant 100.

FIG. 3A is a perspective view of a spacer of an embodiment of implant 100. FIG. 3B and FIG. 3C are cross-sections of the spacer of an embodiment of implant taken at 90° angles respective to each other.

FIG. 4A is a cross-section of an embodiment of implant 100 taken along a plane parallel to the sagittal plane. FIG. 4B is a cross-section of an embodiment of implant corresponding to a plane parallel to the location of the coronal plane, or perpendicular to the sagittal plane of the vertebrae after implant 100 has been inserted.

FIG. 5A and FIG. 5B show perspective views of the first and second inner surfaces of the first end plate and the second end plate of another embodiment of implant 100. FIG. 5C is a cross-section of the embodiment of implant 100 taken along a plane parallel to the sagittal plane. FIG. 5D is a cross-section of the embodiment of implant 100 corresponding to a plane parallel to the location of the coronal plane, or perpendicular to the sagittal plane of the vertebrae after implant 100 has been inserted.

FIG. 6 is a block diagram showing the method steps for the lateral implantation of an embodiment of the disclosed the disclosed implant.

FIG. 7A is a top view of an embodiment of a cutting tool of the invention used to prepare the vertebral bodies for the implant. FIG. 7B is a side view of the embodiment of the cutting tool of the invention from the distal end. FIG. 7C is a distal end view of an embodiment of the cutting tool of the invention.

FIG. 8A is a side view of an embodiment of the implant lateral insertion tool of the invention. FIG. 8B is a top view of the embodiment of the implant lateral insertion tool of the invention. FIG. 8C is a distal end view of the embodiment of the implant lateral insertion tool of the invention. FIG. 8D is a top view of an embodiment of the implant lateral insertion tool holding an embodiment of the implant.

DETAILED DESCRIPTION

The following description is presented to enable any person skilled in the art to make and use what is disclosed. Various modifications to the embodiments described will be readily apparent to those skilled in the art, and the principles defined herein can be applied to other embodiments and applications without departing from the spirit and scope of what is disclosed and defined by the appended claims. Thus, what is disclosed is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein. To the extent necessary to achieve a complete understanding of what is disclosed herein, the specification and drawings of all patents and patent applications cited in this application are incorporated herein by reference.

FIG. 1A shows an embodiment of implant 100. The designations, “A” for anterior, “P” for posterior, “RL” for right lateral, and “LL” for left lateral are given in the drawings for spatial orientation. These designations give the relationship of all faces of implant from the superior perspective; i.e. looking down the axis of the spine. Implant 100 has a first end plate, or upper end plate 110 that is configured to mate with a first vertebra, and a second end plate, or lower end plate 120 that is configured to mate with a second vertebra. A third part 130 that sits between the first end plate 110 and the second end plate 120 is also provided. The third part 130 acts as a spacer between the first end plate 110 and the second end plate 120 and facilitates pivotal or rotational and also twisting movement of the first end plate 110 and the second end plate 120, relative to each other. The third part 130, the spacer, is dimensioned so that it has a curved or convex upper surface and a curved or convex lower surface, as discussed in more detail below.

The upper end plate 110 has a first outer surface 112 from which a first keel 114 extends with a first set of teeth 115. In one embodiment, when implant 100 is inserted between vertebrae, the first keel 114 extends longitudinally across the first outer surface 112, about perpendicular to the sagittal plane of the spine. In another embodiment, the first keel 114 extends longitudinally only partially across the first outer surface 112, about perpendicular to the sagittal plane of the spine. The teeth in the two embodiments with complete or partial extension of the keel across the first outer surface 112 of the upper end plate 110, point towards the left lateral face of implant 100 when the embodiment is meant to be put into a slot in a vertebral body from the left lateral approach to the spine. This orientation is shown in FIG. 1A and FIG. 1B, for example. Alternatively, the teeth 115 point towards the right lateral face of implant 100 when the embodiments are meant to be put into a slot in a vertebral body from the right lateral approach to the spine.

The first outer surface 112 abuts the vertebral body when implant 100 is inserted between vertebrae. The first keel 114 extends into the vertebral body to anchor implant 100 into position, and is perpendicular to the median sagittal plane of the spine, in which extension and flexion occur. The first keel 114 in this orientation offers substantial stability during extension and flexion for implant 100 inserted between the vertebrae of a patient. Additionally, the first keel 114 in this embodiment is aligned with and supports the lateral axis of articulation of implant 100 perpendicular to the sagittal plane of the spine. The first inner surface 116 engages the spacer 130 of implant and opposes the second end plate 120. The first inner surface 116 can form a planar surface that is parallel to the first outer surface 112, or can form a planar surface that is not parallel to the first outer surface 112.

The lower end plate 120 has a second outer surface 122 from which a keel second 124 extends with a second set of teeth 125. In one embodiment, when implant 100 is inserted between vertebrae, the second keel 124 is about perpendicular to the sagittal plane of the spine. As described above for the first upper end plate 110, in one embodiment, the second keel 124 extends longitudinally across the second outer surface 122, while in another embodiment, the second keel 124 extends longitudinally partially across the second outer surface 122. Similarly, the teeth in the two embodiments with complete or partial extension of the keel across the second outer surface 122 of the lower end plate 120 point towards the left lateral face of implant 100 when the embodiment is meant to be put into a slot in a vertebral body from the left lateral approach to the spine. Alternatively, the teeth 125 point towards the right lateral face of implant 100 when the embodiments are meant to be put into a slot in a vertebral body from the right lateral approach to the spine.

The second outer surface 122 abuts the vertebral body when implant 100 is inserted. The second keel 124 extends into the vertebral body to anchor implant 100 into position, and is perpendicular to the median sagittal plane of the spine, in which extension and flexion occur. The second keel 124 in this orientation offers substantial stability during extension and flexion for implant 100 inserted between the vertebrae of a patient. Additionally, the second keel 124 in this embodiment is aligned with and supports the lateral axis of articulation of implant 100 perpendicular to the sagittal plane of the spine. The second inner surface 126, engages the spacer 130 of implant and opposes the first end plate 110. The second inner surface 126 can form a planar surface that is parallel to the second outer surface 122, or can form a planar surface that is not parallel to the second outer surface 122.

The lateral orientation of the first keel 114 and the second keel 124 allow the implant 100 to be inserted into the spine using an advantageous lateral approach as opposed to an anterior or posterior approach. In comparison to a posterior insertion approach in which the spinal nerves can be substantially disturbed, the spinal nerves are bypassed and relatively undisturbed when the implant 100 is inserted laterally between the vertebral bodies from the side of the spine. Although an anterior insertion approach has its benefits, the lateral insertion approach can allow the present implant 100, and associated implantation tools, to be inserted into the spine with less disturbance of the patient's internal organs. This can translate into less time and risk associated with preparing the spine for insertion as well as inserting the implant itself into the spine. Further, the laterally oriented first and second keels 114, 124 offer substantial stability to the vertebral bodies during extension, flexion and lateral bending of the spine.

The first inner surface 116 of the first end plate 110 can be parallel to the second inner surface 126 of the second end plate 120 when implant 100 is assembled and is in a neutral position (i.e., the position where the first end plate 110 has not rotated relative to the second end plate 120). Alternatively, the first inner surface 116 of the first end plate 110 can be non-parallel to the planar surface of the second inner surface 126 of the second end plate 120 when implant 100 is assembled and in a neutral position. This non-parallel orientation of the first end plate 110 and the second end plate 120 allows the plates to pivot to a greater degree with respect to each other. Additionally, other factors such as the height and position of the spacer 130, can also be adjusted in order to increase the degree that the first end plate 110 and the second end plate 120 can pivot relative to each other.

The embodiments shown in FIG. 1 a and FIG. 1 b illustrate the first and second keels 114,124, which include ports 148,152, respectively, that facilitate bone ingrowth. For example, bone from the vertebral bodies can grow thorough the ports 148,152, and aid in securing the first and second keels 114,124 and the implant 100 with respect to the vertebral bodies. In addition, surfaces defined by the first and second keels 114,124 and the first and second outer surfaces 112, 122 of implant 100 can be roughened in order to promote bone ingrowth into these defined surfaces of implant 100. In another embodiment the ports 148,152, the first and second keels 114,124, and the first and second outer surfaces 112, 122 of implant 100 can be coated with materials that promote bone growth such as for example bone morphogenic protein, BMP, or structural materials such as hyaluronic acid, HA, or other substance which promotes growth of bone relative to and into the keel, keel ports, and other external surfaces of the implant 100.

When implant 100 is inserted between vertebrae the planar surfaces corresponding to the first and second outer surfaces 112, 122 and the first and second inner surfaces 116, 126 of the first and second end plates 110, 120 lie within, or substantially within, the axial plane of the body of the patient. Similarly, the first and second keels 114, 124 are aligned in the axial plane, or perpendicular to the sagittal plane of the vertebrae.

FIG. 1B shows an alternative perspective view of implant 100 shown in FIG. 1A. Again, implant 100 has a first or upper end plate 110 that is configured to mate with a first vertebra and a second or lower end plate 120 that is configured to mate with a second vertebra. The first and second keels 114,124 extend into the vertebral bodies to anchor implant 100 into position, and are perpendicular to the median sagittal plane of the spine, in which extension and flexion occur. The first and second keels 114,124 in this orientation offer substantial stability during extension and flexion for implant 100 inserted between the vertebrae of a patient. Additionally, the first and second keels 114,124 in this embodiment are aligned with and support the axis of articulation of implant 100 defined by an RL to LL orientation. The axis of articulation of implant 100 defined by an RL to LL orientation will be discussed in more detail below. The spacer 130 separates the first end plate 110 from the second end plate 120. As evidenced from the perspective view of FIG. 1B, the perimeter shape of the upper and lower end plates 110,120 can be configured to correspond to the perimeter shape of a vertebral disk. As will be appreciated by those of ordinary skill in the art, the perimeter shape of the upper end plate 110 and the lower end plate 120 can be the same.

FIG. 2 a shows a perspective view of an embodiment of the first inner surface 116 of the first or upper end plate 110 of implant 100. The first inner surface 116 of the upper end plate 110 has a first socket or first cavity 210 formed therein. In one embodiment, the first socket 210 has a concave hemi-cylindrical surface. In this embodiment, the first socket 210 includes the shallow concave surface 211 with first ends 213,215 that are substantially perpendicular to the first inner surface 116. Also indicated in FIG. 2 a are two axes, 217,219. The first upper axis 217 intersects the first upper plate 110 in an RL to LL orientation. The second upper axis 219 is perpendicular to the first upper axis 217, and intersects the upper plate 110 in an A to P orientation. The first socket 210 allows the first end plate 110 to pivot or rotate on spacer 130, about a first upper axis 217 that is about perpendicular to the first ends 213,215. The ends 213,215 block motion of the spacer 130 about the second upper axis 219, perpendicular to the first upper axis 217. In this embodiment, it is noted that the first and second keels 114,124 are aligned with and support the first upper axis 217, which is an axis of articulation for first end plate 110 about the spacer 130 for this embodiment, and is an axis that is about perpendicular to the sagittal plane of the spine.

As can be seen in FIG. 2 a, the first socket 210 in this embodiment includes first ends 213,215 that have crests 233,235 respectively. The crests 233,235 project into the first socket 210. Additionally, concave surface 211 has edges 234,236 with crests 237, 239, respectively. The crests 233, 235, 237, and 239 allow a loose fit between the spacer 130 and the first socket 210, which will be disused in more detail below.

FIG. 2 b shows a perspective view of an embodiment of the second or lower end plate 120 of implant 100. The second inner surface 126 of the lower end plate 120 has a second socket or second cavity 240 formed therein. In one embodiment, the second socket 240 has a concave hemi-cylindrical surface. In this embodiment, the second socket 240 includes the shallow concave surface 241 with second ends 243,245 that are substantially perpendicular to the second inner surface 126. Also indicated in FIG. 2 b are two axes, 247,249. The first lower axis 247 intersects the first lower plate 120 in an A to P orientation. The second lower axis 249 is perpendicular to the first lower axis 247, and intersects the lower plate 120 in an RL to LL orientation. As will be described later with respect to the spacer 130, the second socket 240 allows the second end plate 120 to pivot or rotate on spacer 130, about the first lower axis 247 that is about perpendicular to the second ends 243,245. The ends 243,245 block motion of the spacer 130 about the second lower axis 249, perpendicular to the first lower axis 247. In this embodiment, it is noted that the second lower axis 249 is about parallel with first upper axis 217. As previously mentioned, the first and second keels 114,124 are aligned with and support the first upper axis 217, which is an axis of articulation of the upper end plate 110 about the spacer 130 for this embodiment, and is an axis that is about perpendicular to the sagittal plane of the spine, as is second lower axis 249. Further, the first lower axis 247 is an axis of articulation of the lower end plate 120 about the spacer 130, and the first lower axis 247 is perpendicular to the first upper axis 217.

The fit of the spacer in the first socket 210 and the second socket 240 can be loose so that the spacer allows the first end plate 110 to be able to twist somewhat relative to the second plate 120. This twisting action would generally be about an axis that is perpendicular to the first and second inner surfaces 116,126 of the first and second end plates 110,120, respectively. Thus, implant 100 of this embodiment allows the spine to have movement in three orthogonal degrees of freedom, namely (1) forward and backward bending movement, (2) lateral side-to-side bending, and (3) twisting movement. It is to be understood that the second socket 240 in the lower end plate 120 can also have the same design as the first socket 210 in the upper end plate 110 with an increase in the amount of twisting movement afforded by implant 100. As is noted previously herein, loose fit generally between one or both of first socket 210 and second socket 240 and the spacer 130 can allow for twisting motion. Further the spacer 130 can also be made with crests on the curved surfaces and on the ends in order to afford similar twisting motion. In other embodiments, the fit can be tighter in order to restrict such twisting action.

Turning now to FIG. 2 c through FIG. 2 f, the cross-sections of the upper and lower end plates 110,120 of an embodiment of implant 100 are shown. FIG. 2 c illustrates the first dimension 212 of the first socket 210, and FIG. 2 d illustrates the second dimension 214 of the first socket 210. The first dimension 212 and the second dimension 214 of the first socket 210 are perpendicular to each other. FIG. 2 e illustrates that the first dimension 242 of the second socket 240, and FIG. 2 f illustrates the second dimension 244 of the second socket 240. The first dimension 242 and the second dimension 244 of the second socket 240 are perpendicular to each other. FIGS. 2 c and 2 e are a cross-section taken along a plane that would correspond to a plane that is parallel to the median sagittal plane of the body after implant was inserted. FIG. 2 d and FIG. 2 f are a cross-section taken along a plane that would correspond to a plane that is parallel to the frontal (coronal) plane of the body after implant 100 was inserted.

For one embodiment, relative dimensions of the first and second sockets 210,240 are indicated in FIG. 2 c through FIG. 2 f. As previously discussed, the first and second outer surfaces 112,122 of the first and second end plates 110,120 are configured to contact vertebral bodies when implant 100 is inserted between vertebrae. The first and second outer surfaces 112,122 have first and second keels 114,124 that extend into the vertebral body when implant 100 is inserted between vertebrae. The first and second inner surfaces 116,126 of the upper and lower end plates 110,120 have first and second sockets 210,240 formed therein.

In FIG. 2 c, the first socket 210 has a first dimension 212. In the first dimension 212, the first socket 210 is concave such that it is curved like the inner surface of a cylinder. In FIG. 2 d, the second dimension 214 is in the form of a trough or “flattened-U” with a previously indicated concave bottom surface 211 and two ends or sidewalls 213, 215. As shown in FIG. 2 d, the ends or sidewalls 213, 215 are parallel to each other and perpendicular to the bottom surface 211. However, as will be appreciated by those of ordinary skill in the art, the ends or sidewalls 213, 215 can be formed at an angle relative to each other without departing from the scope of what is disclosed.

In FIG. 2 e, the second socket 240 has a first dimension 242. The first dimension 242 is in the form of a trough or “flattened-U” with a bottom concave surface 241 and two ends or sidewalls 243,245. As shown in FIG. 2 f, the ends or sidewalls 243, 245 are parallel to each other and perpendicular to the bottom surface 241. However, as will be appreciated by those of ordinary skill in the art, the ends or sidewalls 243, 245 can be formed at an angle relative to each other without departing from the scope of what is disclosed. In FIG. 2 f, the second dimension 242 of the second socket 240 is concave such that it is curved like the inner surface of a cylinder.

As previously mentioned, FIG. 2 c and FIG. 2 d are oriented to illustrate that the first dimension 212 shown in FIG. 2 c and the second dimension 214 shown in FIG. 2 d are perpendicular to each other, while FIG. 2 e and FIG. 2 f illustrate that the first dimension 242 is perpendicular to second dimension 244. Further, the curved first dimension 212 of FIG. 2 c is oriented perpendicularly to the curved second dimension 244 of FIG. 2 f, while the trough dimension 214 of FIG. 2 d is oriented perpendicularly to the trough dimension 242 of FIG. 2 e. It is noted that in FIGS. 2 c through 2 f that the first inner and second inner surfaces 116,126 of the first and second plates 110,120 are not parallel as shown in FIG. 1 a and FIG. 1 b, for example. In FIGS. 2 c through 2 f the surfaces slope away from the first and second sockets 210,240, respectively, in order to provide for a larger range of motion between the first and second plates.

In FIG. 3 a, the spacer 130 is depicted in perspective view. The spacer 130 is dimensioned so that it has a curved or convex upper surface 310 and a curved or convex lower surface 320, respectively, corresponding with the opposing concave surfaces in the upper end plate 110 and the lower end plate.

As shown in FIG. 3 a, the curved upper surface 310 is bordered along its curved edge by a pair of first sides 312, 314 that are parallel to each other and along its flat edge by a pair of second sides 316, 318 that are parallel to each other and perpendicular to the pair of first sides 312, 314. The orientation of the pair of first sides 312, 314 to the pair of second sides 316, 318 is such that the curved upper edges 322, 324 of the first sides 312, 314 extend toward the ends of the flat edges 321, 323 of the pair of second sides 316, 318. The curved lower edges 326, 328 extend to meet the ends of the flat edges 325, 327 of the first sides 312, 314.

FIG. 3 b and FIG. 3 c show cross-sections of the spacer 130, shown in FIG. 3 a. The cross-section of FIG. 3 b is taken at a 90° angle from the cross-section shown in FIG. 3 c. FIG. 3 b is taken through a plane parallel to the ends 312, 314 and FIG. 3 c is taken through a plane parallel to ends 316, 318. The spacer 130 has a concave upper surface 310 and a concave lower surface 320 and pairs of parallel sides 312, 314 and 314, 318.

FIG. 4 a and FIG. 4 b show sections for an embodiment of implant 100. FIG. 4 a shows a cross-section of implant 100 in its assembled condition taken along a plane that would correspond to a plane that is parallel to the median sagittal plane of the body of a patient after implant 100 was inserted. FIG. 4 b shows a cross-section of implant 100 in its assembled condition taken at 90° from the cross-section shown in FIG. 4 a, which is parallel to the frontal (coronal) plane, or perpendicular to the sagittal plane of the body of a patient after implant 100 was inserted. The implant 100 has a first upper end plate 110 that is configured to mate with a first vertebra and a second lower end plate 120 that is configured to mate with a second vertebra. The spacer 130 sits between the upper end plate 110 and the lower end plate 120. As previously mentioned, the first upper axis 217 is an axis of articulation for first end plate 110 about the spacer 130 for this embodiment, while the first lower axis 247 is an axis of articulation of the lower end plate 120 about the spacer 130. Further, first upper axis 217 is perpendicular to the first lower axis 247. FIG. 4 a, in particular, indicates how the first and second keels, 114,124, are aligned with and support the lateral axis of articulation defined by the first upper axis 217. The first and second keels 114,124 in this orientation offers substantial stability during extension and flexion for implant 100 inserted between the vertebrae of a patient. As in all of the embodiments described herein, the keels are about perpendicular to the sagittal plane of the body of a patient and suitable for lateral insertion into the spine of a patient.

FIG. 5 a through FIG. 5 c show representations for an another embodiment of implant 100. FIG. 5 a and FIG. 5 b show the first and second inner surfaces, 116,126, of the first and second endplates of another embodiment of implant 100. It should be noted that this additional embodiment of Implant 100 has the features described previously described for FIG. 2 a and FIG. 2 b. Similarly, FIG. 5 c and FIG. 5 d are sections that are analogous to the sections of a first embodiment shown for FIG. 4 a and FIG. 4 b, respectively.

FIG. 5 a shows a perspective view of an embodiment of the first inner surface 116 of the first or upper end plate 110 of implant 100. The first inner surface 116 of the upper end plate 110 has a first socket or first cavity 210 formed therein. In the embodiment of FIG. 5 a, the first socket 210 has a concave hemispherical surface. Indicated in FIG. 5 a are two axes, 217,219. The first upper axis 217 intersects the first upper plate 110 in an RL to LL orientation. The second upper axis 219 is perpendicular to the first upper axis 217, and intersects the upper plate 110 in an A to P orientation. The two axes intersect at first, or upper point 119. The first socket 210 allows the first end plate 110 to pivot or rotate on spacer 130 about the first point 119. FIG. 5 b shows a perspective view of an embodiment of the second inner surface 126 of the second or lower end plate 120 of implant 100. The second inner surface 126 of the lower end plate 120 has a second socket or first cavity 240 formed therein. In the embodiment of FIG. 5 b, the second socket 240 has a concave hemispherical surface. Indicated in FIG. 5 b are two axes, 247,249. The first lower axis 247 intersects the second, or lower plate 120 in an RL to LL orientation. The second lower axis 249 is perpendicular to the first upper axis 247, and intersects the lower plate 120 in an A to P orientation. The two axes intersect at second, or lower point 121. The second socket 240 allows the second lower end plate 120 to pivot or rotate on spacer 130, about the lower point 121.

In the alternative embodiment shown in FIG. 5 a and FIG. 5 b, it is noted that the first and second keels 114,124 are aligned with and support the first and second points and 119, 121, which are an points of articulation for first end plate 110 and the second end plate, respectively about the spacer 130 for this embodiment. The keels are oriented so as to be about perpendicular to the sagittal plane of a patient when the implant is inserted using a lateral approach.

FIG. 5 c shows a cross-section of implant 100 in its assembled condition taken along a plane that would correspond to a plane that is parallel to the median sagittal plane of the body of a patient after implant 100 was inserted. FIG. 5 d shows a cross-section of implant 100 in its assembled condition taken at 90° from the cross-section shown in FIG. 5 c, which is parallel to the frontal (coronal) plane, or perpendicular to the sagittal plane of the body of a patient after implant 100 was inserted. The implant 100 has a first upper end plate 110 that is configured to mate with a first vertebra and a second lower end plate 120 that is configured to mate with a second vertebra. The spacer 130 sits between the upper end plate 110 and the lower end plate 120. As previously mentioned, the first and second upper axes 217,219 define a first point of articulation for first end plate 110 about the spacer 130 for this embodiment, while the first and second lower axes 247,249 define a second point of articulation of the lower end plate 120 about the spacer 130. FIG. 5 c and FIG. 5 d indicate how the first and second keels, 114,124, are aligned with and support the first and second points of articulation 119,121. The first and second keels 114,124 in this orientation offer substantial stability during extension and flexion for implant 100 inserted between the vertebrae of a patient.

It is to be understood that the embodiments of the disclosed implant can be made of medical grade titanium, stainless steel or cobalt chrome. Other materials that have appropriate structural strength and that are suitable for implantation into a patient can also be used.

Alternatively, the spacer 130 can be made out of a polymer, and more specifically, the polymer is a thermoplastic with the other components made of the materials specified above. Still more specifically, the polymer is a polyketone known as polyetheretherketone (PEEK). Still more specifically, the material is PEEK 450G, which is an unfilled PEEK approved for medical implantation available from Victrex of Lancashire, Great Britain. (Victrex is located at www.matweb.com or see Boedeker www.boedeker.com). Other sources of this material include Gharda located in Panoli, India (www.ghardapolymers.com). The spacer 130 can be formed by extrusion, injection, compression molding and/or machining techniques. This material has appropriate physical and mechanical properties and is suitable for carrying and spreading the physical load between the spinous process. Further in this embodiment, the PEEK has the following additional approximate properties:

Property Value Density 1.3 g/cc Rockwell M 99 Rockwell R 126 Tensile Strength 97 Mpa Modulus of Elasticity 3.5 Gpa Flexural Modulus 4.1 Gpa

It should be noted that the material selected may also be filled. For example, other grades of PEEK are also available and contemplated, such as 30% glass-filled or 30% carbon-filled, provided such materials are cleared for use in implantable devices by the FDA, or other regulatory body. Glass-filled PEEK reduces the expansion rate and increases the flexural modulus of PEEK relative to that which is unfilled. The resulting product is known to be ideal for improved strength, stiffness, or stability. Carbon-filled PEEK is known to enhance the compressive strength and stiffness of PEEK and lower its expansion rate. Carbon-filled PEEK offers wear resistance and load carrying capability.

The spacer can also be comprised of polyetherketoneketone (PEKK). Other material that can be used include polyetherketone (PEK), polyetherketoneether-ketoneketone (PEKEKK), and polyetheretherketoneketone (PEEKK), and, generally, a polyaryletheretherketone. Further, other polyketones can be used as well as other thermoplastics.

Reference to appropriate polymers that can be used in the spacer can be made to the following documents, all of which are incorporated herein by reference. These documents include: PCT Publication WO 02/02158 A1, dated Jan. 10, 2002, entitled “Bio-Compatible Polymeric Materials;” PCT Publication WO 02/00275 A1, dated Jan. 3, 2002, entitled “Bio-Compatible Polymeric Materials;” and, PCT Publication WO 02/00270 A1, dated Jan. 3, 2002, entitled “Bio-Compatible Polymeric Materials.”

In operation, implant 100 enables a forward bending movement and a rearward bending movement by sliding the upper end plate 110 forward and backward over the spacer 130 relative to the lower end plate 120. This movement is shown as rotation about the axis 217 in FIG. 4 a and FIG. 4 c.

The implant 100 enables a right lateral bending movement and a left lateral bending movement by sliding the lower end plate 120 side-to-side over the spacer 130 relative to upper end plate 110. This movement is shown as rotation about the axis 219 in FIG. 4 b and FIG. 4 d. Additionally, with a loose fit between the first end plate, the second end plate and the spacer, rotational or twisting motion along an axis that is along the spine and perpendicular to the first and second plates is accomplished.

FIG. 6 is a block diagram showing the basic steps of the method of laterally inserting the implant 100. First the spine is exposed through a lateral access 610, then the intervertebral disk is removed if necessary laterally 620. The implant is then inserted laterally 630 between two vertebrae and the wound is closed 640. This procedure can be followed for either a left lateral approach or right lateral approach. For a left lateral approach, the teeth 115,125 of upper and lower keels 114, 124 would be pointed towards the left lateral face of the device in order to aid in retaining implant 100 in place. For a right lateral approach, the teeth would point towards the right lateral face of the device.

Additional steps, such as cutting channels into the vertebral bodies to accept the first and second keels 114,124 of the first and second end plates 110,120 and assembling implant 100 by inserting the spacer 130 between the upper and lower end plates 110,120 prior to installation can also be performed without departing from the scope of what is disclosed.

It is to be appreciated that although the first and second plates are depicted as having concave cavities and the spacer is depicted as having two convex surfaces that are oriented about perpendicular to each other, that other embodiments the disclosed implant can have other configurations. For example, the first and second plates can have convex protrusions, such as, for example, cylindrical protrusions that are shaped to mate with concave surfaces of a spacer, with the concave surfaces of the spacer oriented about perpendicular to each other. In this embodiment, the convex protrusions of the first and the second plates could preferably each have a pair of parallel side walls that would act as the side walls in the depicted embodiments in order to block motion of the spacer. Also, it is to be appreciated that in still another embodiment, the spacer can have upper and lower truncated convex spherical surfaces with two pairs of side walls, instead of cylindrical surfaces with side walls, and be in the scope and spirit of what is disclosed herein. In this embodiment, each of the first and second plates would have truncated concave spherical surfaces with a pair of side walls. In still a further embodiment, each of the first and second plates could have spherical protrusions with a pair of side walls and the spacer could have first and second spherical concave surfaces with two pairs of side walls joining the first and second spherical concave surfaces. Still alternatively, the first end plate can have a concave surface and blocking side walls and the mating portion of the spacer can be convex with the second plate having a convex protrusion with the mating portion of the spacer, or being concave, with blocking side walls.

What has been disclosed herein has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit what is disclosed to the precise forms described. Many modifications and variations will be apparent to the practitioner skilled in the art. What is disclosed was chosen and described in order to best explain the principles and practical application of the embodiments described herein, thereby enabling others skilled in the art to understand the various embodiments and various modifications that are suited to the particular use contemplated. It is intended that the scope of what is disclosed be defined by the following claims and their equivalence.

FIG. 7A is a top view of an embodiment of a cutting tool of the invention used to prepare the vertebral bodies for the implant. FIG. 7B is a side view of the embodiment of the cutting tool of the invention from the distal end. FIG. 7C is a distal end view of an embodiment of the cutting tool of the invention.

FIG. 8A is a side view of an embodiment of the implant lateral insertion tool of the invention. FIG. 8B is a top view of the embodiment of the implant lateral insertion tool of the invention. FIG. 8C is a distal end view of the embodiment of the implant lateral insertion tool of the invention. FIG. 8D is a top view of an embodiment of the implant lateral insertion tool holding an embodiment of the implant.

The lateral orientation of the keels allow the implants to be inserted into the spine using a lateral approach as opposed to an anterior or posterior approach. The lateral approach is advantageous, because the spinal nerves in the spinal cavity are minimally undisturbed when the implants are inserted laterally into the spine. In comparison to a posterior insertion approach in which the spinal nerves can be substantially disturbed, the spinal nerves are bypassed and relatively undisturbed when the implant is inserted laterally between the vertebral bodies from the side of the spine. Although an anterior insertion approach has its benefits, the lateral insertion approach can allow the present implant and associated implantation tools, to be inserted into the spine with less disturbance of the patient's internal organs. This can translate into less time and risk associated with preparing the spine for insertion as well as inserting the implant itself into the spine. Further, the laterally oriented keels offer substantial stability to the vertebral bodies during extension, flexion and lateral bending of the spine.

FIG. 7A through FIG. 7C are the top view, the side view, and an end view of the cutting tool 700. The cutting tool 700 has a handle 710 at its proximal end for controlling the tool during operation. As will be appreciated by those of skill in the art, the handle 710 can be removable or affixed to the cutting end. The distal end 702 of the tool 700 is solid head has an upper surface 705, and a lower surface 706. The upper surface 705 has a first blade 712 mounted thereon, and the lower surface 706 has a second blade 714 mounted thereon. Preferably the first blade 712 is about centered with the upper surface 705, and the second blade 714 is about centered with the lower surface 706. The first and second blades 712, 714 are oriented to cut a space in a first and second intervertebral body for the first and second keels 114, 124 of implants 100, 600. The space is perpendicular to the sagittal plane of the vertebrae, and allows for the lateral insertion of the implants 100, 600. FIG. 7C is a view of the distal end of the cutting tool 700 showing the beveled end 716 and the first and second blades 712, 714. The height h of the head 702 of the cutting tool 700 approximates the distance between two vertebral bodies or the height of the disk space. In this embodiment of cutting tool 700, the blades 712, 714 extend above and below the head 702.

As will be appreciated by those of skill in the art, the tool shown in FIG. 7A can be modified such that instead of cutting keel-receiving channels in the upper and lower vertebral bodies at the same time, two tools are provided so that only one vertebral body is cut for keel-receiving channels at a time. For example, an alternative embodiment of cutting tool 700 has a first tool with a single blade mounted on the head 702. A second tool could be provided having a single blade mounted on the head 702, and additionally on the opposing surface, a guide. The guide on the surface opposite the surface with the blade is designed to engage with the first keel receiving channel cut the first vertebrae with the first tool to ensure that the second cut is optimally aligned with the first cut.

FIG. 8A through FIG. 8D depict an embodiment of the implanting tool used to insert the implant 600 of FIG. 6A between vertebral bodies. FIG. 8A is a side view of the implantation tool 800 that has a handle 810 and an implant holder 820. The implant holder 820 has an implant conforming surface 824 and four pins 822 for holding the first end plate 610 and the second end plate 620 implant 600. The conforming surface 824 is curved to follow the convex outer LL edges of the first and second end plates 610, 620, respectively, for an implant inserted from the left lateral side of a patient. The implant 600 nests within a conforming surface 824 and is held by pins 822. FIG. 8C shows the distal view of the end of the tool with four pins 822 for securing the first and second end plate of the implant. 

1. A method of inserting an implant comprising: a. accessing a lateral side of an upper vertebral body and a lower vertebral body; b. using a tool to cut a first lateral keel receiving channel into the upper vertebral body from a lateral approach, wherein the first keel receiving channel extends between a first lateral side and a second lateral side of the vertebral body and simultaneously using the tool to cut a second lateral keel receiving channel into the lower vertebral body from a lateral approach, wherein the second keel receiving channel is substantially parallel to the first keel receiving channel, wherein the tool does not have a power supply; and c. inserting a first keel of an implant into the first keel receiving channel and a second keel of the implant into the second keel receiving channel from a lateral approach, wherein the implant includes a spacer having upper and lower cylindrically curved surfaces oriented perpendicular to one another; wherein the implant comprises a first end plate having a first outer surface and an opposing first inner surface, the first inner surface comprising a first socket having a concave hemi-cylindrical surface bounded by a pair of planar end surfaces, each of the end surfaces extending substantially perpendicular to the inner surface, wherein the end surfaces prevent motion of the first end plate relative to the spacer about a first axis extending substantially parallel to the end surfaces and wherein the concave hemi-cylindrical surface permits motion of the first end plate relative to the upper cylindrically curved surface of the spacer about a second axis substantially perpendicular to the first axis, and wherein the first keel extends from the outer surface of the first end plate substantially parallel to the second axis; and wherein the implant comprises a second end plate having a second outer surface and an opposing second inner surface, the second inner surface comprising a second socket having a concave hemi-cylindrical surface bounded by a pair of planar end surfaces, each of the end surfaces extending substantially perpendicular to the inner surface and the second axis, wherein the end surfaces prevent motion of the second end plate relative to the spacer about the second axis and wherein the concave hemi-cylindrical surface permits motion of the second end plate relative to the lower cylindrically curved surface of the spacer about the first axis, and wherein the second keel extends from the outer surface of the second end plate substantially parallel to the second axis.
 2. The method of claim 1 wherein the first and second keels are oriented substantially perpendicular to a sagittal plane of the vertebral bodies when inserted therein.
 3. The method of claim 1 further comprising assembling the implant prior to inserting the implant between the upper and lower vertebral bodies.
 4. The method of claim 1 further comprising assembling the implant subsequent to inserting the implant between the upper and lower vertebral bodies.
 5. The method of claim 1 wherein the first keel further comprises a plurality of teeth each having an angled side facing the keel receiving channel when the implant is inserted therein.
 6. The method of claim 1 wherein the second keel further comprises a plurality of teeth each having an angled side facing the keel receiving channel when the implant is inserted therein.
 7. The method of claim 1 further comprising assembling the implant including: selecting the first end plate having the first keel extending from the first outer surface and the first socket in the first inner surface; selecting the second end plate having the second keel extending from the second outer surface and the second socket in the second inner surface; and positioning the spacer between the first end plate and the second end plate wherein the upper cylindrically curved surface is positioned in the first socket and the lower cylindrically curved surface is positioned in the second socket.
 8. The method of claim 1, wherein the concave hemi-cylindrical surface of the first socket defines a first pair of edges having a first pair of crests projecting inwardly into the first socket and wherein the pair of planar end surfaces of the first socket define a second pair of edges having a second pair of crests projecting inwardly into the first socket, the first and second pairs of crests providing a loose fit between the spacer and the first end plate allowing rotation of the first end plate relative to the spacer about a third axis perpendicular to both of the first and second axes.
 9. The method of claim 8, wherein the concave hemi-cylindrical surface of the second socket defines a third pair of edges having a third pair of crests projecting inwardly into the second socket and wherein the pair of planar end surfaces of the second socket define a fourth pair of edges having a fourth pair of crests projecting inwardly into the second socket, the third and fourth pairs of crests providing a loose fit between the spacer and the second end plate allowing rotation of the second end plate relative to the spacer about the third axis.
 10. A method of inserting an intervertebral implant in a spine comprising: a. using a tool from a lateral approach to prepare an affected area of the spine to receive the implant by simultaneously cutting first and second lateral receiving channels into upper and lower vertebral bodies, wherein the tool does not have a power supply; and b. simultaneously inserting a first keel of an implant into the upper vertebral body of the affected area from a lateral approach, and a second keel of an implant into the lower vertebral body of the affected area from a lateral approach, wherein the first keel extends between a first lateral end and a second lateral end of the implant, wherein the second keel extends between a first lateral end and a second lateral end of the implant, the implant comprising an upper endplate having inwardly facing upper cylindrically curved endplate surface and a lower endplate having a inwardly facing lower cylindrically curved endplate surface, the endplate surfaces oriented perpendicular to one another, the upper endplate surface extending along a first axis and the lower endplate surface extending along a second axis substantially perpendicular to the first axis, the implant further comprising a spacer having upper and lower cylindrically curved spacer surfaces oriented perpendicular to one another along the first and second axes, respectively, for movably engaging the upper and lower endplate surfaces, wherein at least one pair of edges of the upper endplate surface defines a pair of crests extending inwardly into the upper endplate surface such that engagement between the spacer and the first endplate surface is loose to allow rotation of the upper endplate relative to the spacer about a third axis perpendicular to both of the first and second axes.
 11. A method of inserting an intervertebral implant in a spine comprising: a. using a tool from a lateral approach to prepare an affected area of the spine to receive the implant by simultaneously cutting first and second lateral receiving channels into upper and lower vertebral bodies, wherein the tool does not have a power supply; and b. simultaneously inserting a first keel of an implant into the upper vertebral body of the affected area, and a second keel of an implant into the lower vertebral body of the affected area from a lateral approach, wherein the implant has a spacer having convex upper and lower cylindrically curved surfaces oriented perpendicular to one another: wherein the implant comprises a first end plate having a first outer surface and an opposing first inner surface, the first inner surface comprising a first socket having a concave partially cylindrical surface bounded by a pair of planar end surfaces, each of the end surfaces extending substantially perpendicular to the inner surface, wherein the end surfaces prevent motion of the first end plate relative to the spacer about a first axis extending substantially parallel to the end surfaces and wherein the concave partially cylindrical surface permits motion of the first end plate relative to the upper cylindrically curved surface of the spacer about a second axis substantially perpendicular to the first axis, and wherein the first keel extends from the outer surface of the first end plate substantially parallel to the second axis; and wherein the implant comprises a second end plate having a second outer surface and an opposing second inner surface, the second inner surface comprising a second socket having a concave partially cylindrical surface bounded by a pair of planar end surfaces, each of the end surfaces extending substantially perpendicular to the inner surface and the second axis, wherein the end surfaces prevent motion of the second end plate relative to the spacer about the second axis and wherein the concave partially cylindrical surface permits motion of the second end plate relative to the lower cylindrically curved surface of the spacer about the first axis, and wherein the second keel extends from the outer surface of the second end plate substantially parallel to the second axis.
 12. The method of claim 11, wherein the concave partially cylindrical surface of the first socket defines a first pair of edges having a first pair of crests projecting inwardly into the first socket and wherein the pair of planar end surfaces of the first socket define a second pair of edges having a second pair of crests projecting inwardly into the first socket, the first and second pairs of crests providing a loose fit between the spacer and the first end plate allowing rotation of the first end plate relative to the spacer about a third axis perpendicular to both of the first and second axes.
 13. The method of claim 12, wherein the concave partially cylindrical surface of the second socket defines a third pair of edges having a third pair of crests projecting inwardly into the second socket and wherein the pair of planar end surfaces of the second socket define a fourth pair of edges having a fourth pair of crests projecting inwardly into the second socket, the third and fourth pairs of crests providing a loose fit between the spacer and the second end plate allowing rotation of the second end plate relative to the spacer about the third axis.
 14. The method of claim 11 further comprising assembling the implant prior to inserting the implant between the upper and lower vertebral bodies.
 15. The method of claim 14 wherein assembling the implant comprises: obtaining a first end plate having the first keel extending from the first outer surface and the first socket in the first inner surface; obtaining a second end plate having the second keel extending from the second outer surface and the second socket in the second inner surface; obtaining a spacer having convex upper and lower cylindrically curved surfaces oriented perpendicular to one another; and positioning the spacer between the first end plate and the second end plate such that the upper cylindrically curved surface is positioned in the first socket and the lower cylindrically curved surface is positioned in the second socket.
 16. The method of claim 11 further comprising assembling the implant subsequent to inserting the implant between the upper and lower vertebral bodies.
 17. The method of claim 16 wherein assembling the implant comprises: obtaining a first end plate having the first keel extending from the first outer surface and the first socket in the first inner surface; obtaining a second end plate having the second keel extending from the second outer surface and the second socket in the second inner surface; obtaining a spacer having convex upper and lower cylindrically curved surfaces oriented perpendicular to one another; and positioning the spacer between the first end plate and the second end plate such that the upper cylindrically curved surface is positioned in the first socket and the lower cylindrically curved surface is positioned in the second socket.
 18. A method of inserting an intervertebral implant in a spine comprising: a. using a tool from a lateral approach to prepare an affected area of the spine to receive the implant by simultaneously cutting first and second lateral receiving channels into upper and lower vertebral bodies, wherein the tool does not have a power supply; and b. simultaneously inserting a first keel of an implant into the upper vertebral body of the affected area, and a second keel of an implant into the lower vertebral body of the affected area from a lateral approach so that an angled side of each tooth of a plurality of teeth of one or both of the first and second keels faces the respective one or both of the first and second lateral receiving channels as the one or both of the first and second keels are inserted therein, the first keel extending from a first outer surface of the implant and the second keel extending from a second outer surface of the implant, each of the respective plurality of teeth having a height less than the height of the respective one or both first and second keels, and the first and second keels each having a body portion and a plurality of teeth portion, the plurality of teeth portion extending along the body portion, the body portion separating the plurality of teeth portion from the respective first and second outer surfaces; wherein the implant comprises: a spacer having convex upper and lower partially cylindrically curved surfaces oriented substantially perpendicular to one another; a first end plate having the first outer surface and an opposing first inner surface, the first inner surface comprising a first socket having a concave partially cylindrical surface bounded by a pair of planar end surfaces, each of the end surfaces extending substantially perpendicular to the inner surface, wherein the end surfaces prevent motion of the first end plate relative to the spacer about a first axis extending substantially parallel to the end surfaces and wherein the concave partially cylindrical surface permits motion of the first end plate relative to the upper cylindrically curved surface of the spacer about a second axis substantially perpendicular to the first axis, and wherein the first keel extends from the outer surface of the first end plate substantially parallel to the second axis; and wherein the implant comprises a second end plate having the second outer surface and an opposing second inner surface, the second inner surface comprising a second socket having a concave partially cylindrical surface bounded by a pair of planar end surfaces, each of the end surfaces extending substantially perpendicular to the inner surface and the second axis, wherein the end surfaces prevent motion of the second end plate relative to the spacer about the second axis and wherein the concave partially cylindrical surface permits motion of the second end plate relative to the lower cylindrically curved surface of the spacer about the first axis, and wherein the second keel extends from the outer surface of the second end plate substantially parallel to the second axis.
 19. The method of claim 18 further comprising assembling the implant prior to inserting the implant between the upper and lower vertebral bodies.
 20. The method of claim 19 wherein assembling the implant comprises: obtaining a first end plate having the first keel extending from the first outer surface and the first socket in the first inner surface; obtaining a second end plate having the second keel extending from the second outer surface and the second socket in the second inner surface; obtaining a spacer having convex upper and lower partially cylindrically curved surfaces oriented perpendicular to one another; and positioning the spacer between the first end plate and the second end plate such that the upper partially cylindrically curved surface is positioned in the first socket and the lower partially cylindrically curved surface is positioned in the second socket.
 21. The method of claim 18 further comprising assembling the implant subsequent to inserting the implant between the upper and lower vertebral bodies.
 22. The method of claim 21 wherein assembling the implant comprises: obtaining a first end plate having the first keel extending from the first outer surface and the first socket in the first inner surface; obtaining a second end plate having the second keel extending from the second outer surface and the second socket in the second inner surface; obtaining a spacer having convex upper and lower partially cylindrically curved surfaces oriented perpendicular to one another; and positioning the spacer between the first end plate and the second end plate such that the upper partially cylindrically curved surface is positioned in the first socket and the lower partially cylindrically curved surface is positioned in the second socket. 